1988 20LG rough idle.

[panasonic]

The engine is:

1988 20LG

6L3 L 300338

After several short trips in my boat, this engine runs very good Except right at idle. Any throttle setting above that is good.

As I am planning on doing some *****ing with this engine I really would like it to idle as smooth as possible, and as slow as possible.

The engine has been gone thru several times now to fix a misfire last year, please see: http://www.yamahaoutboardparts.com/f...e-th27529.html (I know wrong year, didn't know how to change it)

Been fooling with Idle mixture screws but it persists...

Please see following videos. First one is the rough idle about 20 seconds in.

The second is just one of everything up to wide open.


https://www.youtube.com/watch?v=T54k3BUqMYY&t=2s


https://www.youtube.com/watch?v=BuMcwkBVQdw


I know its not the CDI...lol

[99yam40]

upper of lower crank seals
re-circulation check valves maybe if it has them
other gaskets/seals

carb problems

[panasonic]

upper of lower crank seals
re-circulation check valves maybe if it has them
other gaskets/seals

carb problems

It seems like the bottom cylinder to me, that plug always seems to be darker then the top.

If its a carb problem, I don't know what it could be, I bet I had them off 5 or 6 times and they were clean the first time, and I mean clean like new clean. But I disassembled them any way and blew them out, wired every passage. Fuel pump was rebuilt, it is on the bottom carb.

Only time I ever ran across a two stroke acting like that was a few snowmobiles with a bad crank seal...or a partially plugged idle jet.

[99yam40]

would not hurt to look at the pump again just in case

[panasonic]

I thought the same and replaced the fuel pump diaphragm twice and inspected the the little one way valves closely. All seemed well .

Going out to go out again today and fool with it some more.

BTW I looked at the top crank seal when I had fly wheel off and it looked fine. The bottom crank seal I can just see and put propane to that one while engine running to see if it would suck any propane and speed up. No evidence of leaking at the seals. hmmmm

[panasonic]

Out in boat today again trying to get my engine to idle properly. Did the following:

-Checked timing while running from idle all the way till fully advanced. Checks good.

- adjusted mixture screws more times than I care to tell both in and out from initial settings, with a little burst of speed between each setting, then back to idle.

- checked both plugs several times, nice light tan colour.

- pumped primer ball when at idle and running rough to see if it starving for fuel. No change.

The engine will idle for long periods of time without shutting off but it just keeps stumbling over and over in the same pattern. Almost like a misfire. Any thing just off idle and above and it works perfectly.

It seems like after I go for a couple minutes at speed then slow back down to idle.. it will idle smoothly for probably 20 seconds then start stumbling again.

Starting to torment me now...